Embodiments of the invention relate generally to an MR system and, more particularly, to an RF coil having enhanced acoustic deadening properties.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals is digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
In existing MR systems, one problem that is encountered is the loud acoustic noise generated by the system. The noise level generated by the MR system can become uncomfortably loud, both for the patient, or subject, and for the operators. The source of such acoustic noise can be many and varied, however, in general, the noise can be attributed to vibration of an RF coil included in the MR system that surrounds the subject whose purpose is to direct RF energy toward the subject or receive RF energy from the subject, in carrying out the scanning process. The noise/vibration from the RF coil is due to Lorentz forces applied to a gradient coil of the MR system that result from an interaction of a static magnetic field and electrical current, with the Lorentz forces thereby creating vibrations in the gradient coil. The vibrations Structural borne and airborne noise generated in the gradient coil from the vibrations reach the RF body coil, which in turn vibrates and consequently radiates acoustic noise into the patient bore of the MR system.
The acoustic noise from the RF coil is difficult to control due to its close proximity to the patient, or subject, bore. There have been attempts at reducing the acoustic noise from the RF coil. Such attempts have included breaking up the RF conductor, where possible, to reduce eddy currents and constrained layer damping to reduce the RF support form vibration. These attempts, however, have not been able to eliminate all of the acoustic noise from the RF coil.
It would therefore be desirable to have an RF coil having a reduced acoustic output by providing vibration isolation between the RF conductors and the RF support form as well as providing damping to reduce the vibration from the RF conductor to the RF support form.